The commercial preparation of most linear condensation polymers such as polyamides or polyesters involves heating monomeric starting materials to cause progressive condensation with loss of low molecular weight volatile material until the desired molecular weight level is achieved. The process is usually carried out in two or more stages with intermediate formation of a low molecular weight, low viscosity polymeric liquid which is then passed through finishing vessels which are maintained at proper temperatures and low pressures.
The problems associated with the proper design of polymer finishers have been recognized and described in the prior art. A finisher such as that illustrated by Ferrante in FIG. 1 of U.S. Pat. No. 3,361,537 functions to produce polymer with uniform viscosity. However, it has been found that gel builds up behind the struts that support the spiral ribbon agitator, particularly where the struts are attached to the ribbon flight. The polymer is highly viscous at this 5 point in the process and stagnates in areas directly behind the struts and adjacent to the ribbon flight surface. The gel builds up in time to such an extent that portions break loose, drop into the melt and are carried off into the polymer stream. The gel slough is subsequently subdivided into smaller particles as it passes through the various downstream pumps and ultimately is fed to the spinning machine where it causes serious discontinuties. To avoid the effects of gel sloughs, finishers must be cleaned at rather frequent intervals. This is costly and, since a slough cannot be predicted, a scheduled finisher clean-up often fails to avert a process upset.